Method and apparatus for reducing phase imbalance in radio frequency signals

Abstract

Systems and method for reducing phase imbalance in radio frequency (RF) signals are disclosed. The phase imbalance in an RF signal may be due to phase imbalance in the local oscillator used for upconversion in a transmitter, and downconversion in a receiver. The RF signal is converted to a digital signal. The phase imbalance in the digital signal is measured by using a digital signal processor. The digital signal processor generates a compensation signal in response to the measurement of the phase imbalance. The compensation signal is used to generate a tuning signal to tune the local oscillator used for the upconversion or downconversion, thereby reducing the phase imbalance.

1 . A communication system capable of reducing phase imbalance between an in-phase component and a quadrature component of a communication signal, the communication system comprising: 
 a transmitter capable of generating a radio frequency (RF) signal from the in-phase component and the quadrature component by using a first quadrature local oscillator signal;    a receiver capable of receiving the RF signal, and downconverting the RF signal to obtain the in-phase component and the quadrature component using a second quadrature local oscillator signal, wherein the second quadrature local oscillator signal is provided by a low-error quadrature local oscillator;    a digital signal processor capable of generating the in-phase component and the quadrature component, and measuring the phase imbalance between the in-phase component and the quadrature component upon downconverting the RF signal; and    a quadrature corrector capable of providing a phase correction between the in-phase component and the quadrature component based on the phase imbalance by varying the first quadrature local oscillator signal.    
   
   
       2 . The communication system according to  claim 1 , wherein the transmitter comprises an upconverter capable of upconverting the communication signal to the RF signal using the first quadrature local oscillator signal.  
   
   
       3 . The communication system according to  claim 1 , wherein the receiver comprises a downconverter capable of downconverting the RF signal to obtain the in-phase component and the quadrature component using the second quadrature local oscillator signal.  
   
   
       4 . The communication system according to  claim 1 , wherein the receiver further comprises a cartesian feedback block.  
   
   
       5 . The communication system according to  claim 1 , wherein the low-error quadrature local oscillator is at least one of a) an external local oscillator and b) an internal local oscillator.  
   
   
       6 . The communication system according to  claim 1 , wherein the digital signal processor is further capable of generating a compensation signal in response to measuring the phase imbalance.  
   
   
       7 . The communication system according to  claim 6 , wherein the quadrature corrector generates a tuning signal based on the compensation signal to vary the first quadrature local oscillator signal.  
   
   
       8 . The communication system according to  claim 1 , wherein the digital signal processor comprises: 
 a first analog to digital converter for converting the in-phase component from the receiver to a digital in-phase feedback component;    a second analog to digital converter for converting the quadrature component from the receiver to a digital quadrature feedback component; and    a digital quadrature evaluator for measuring the phase imbalance between the digital in-phase feedback component and the digital quadrature feedback component to generate the compensation signal.    
   
   
       9 . The communication system according to  claim 8 , wherein the digital signal processor further comprises: 
 a first digital to analog converter for generating the in-phase component of the communication signal from a digital in-phase component; and    a second digital to analog converter for generating the quadrature component of the communication signal from a digital quadrature component.    
   
   
       10 . The communication system according to  claim 9 , wherein the digital quadrature evaluator comprises a digital comparator for measuring the phase imbalance between the digital in-phase feedback component and the digital quadrature feedback component by comparing the digital in-phase feedback component with the digital in-phase component, and the digital quadrature feedback component with the digital quadrature component.  
   
   
       11 . A communication system capable of reducing phase imbalance between an in-phase component and a quadrature component of a radio frequency (RF) signal, the communication system comprising: 
 a receiver capable of receiving the RF signal, and downconverting the RF signal using a quadrature local oscillator signal to obtain the in-phase component and the quadrature component in baseband;    a digital signal processor capable of measuring the phase imbalance between the in-phase component and the quadrature component in baseband; and    a quadrature corrector capable of providing a phase correction between the in-phase component and the quadrature component in baseband based on the phase imbalance between the in-phase component and the quadrature component in baseband by varying the quadrature local oscillator signal.    
   
   
       12 . The communication system according to  claim 11 , further comprising an RF signal generator for generating and transmitting the RF signal.  
   
   
       13 . The communication system according to  claim 11 , further comprising a divide down reference to obtain the RF signal by dividing a high frequency signal.  
   
   
       14 . The communication system according to  claim 11 , wherein the receiver comprises a downconverter for downconverting the RF signal to obtain the in-phase component and the quadrature component in baseband using the quadrature local oscillator signal.  
   
   
       15 . The communication system according to  claim 1   1 , wherein the digital signal processor is further capable of generating a compensation signal in response to measuring the phase imbalance.  
   
   
       16 . The communication system according to  claim 15 , wherein the digital signal processor comprises: 
 a first analog to digital converter for converting the in-phase component in baseband to a digital in-phase feedback component;    a second analog to digital converter for converting the quadrature component in baseband to a digital quadrature feedback component; and    a digital quadrature evaluator for measuring the phase imbalance between the digital in-phase feedback component and the digital quadrature feedback component to generate the compensation signal.    
   
   
       17 . A method for reducing phase imbalance in a radio frequency (RF) signal, the RF signal comprising an in-phase component and a quadrature component, the method comprising: 
 receiving the RF signal;    downconverting the RF signal to obtain the in-phase component and the quadrature component in baseband, using a quadrature local oscillator signal, wherein the in-phase component is associated as a reference signal and the quadrature component comprises three signals approximately 90, 180, and 270 degrees phase shifted relative to the reference signal;    detecting the phase imbalance between the in-phase component and the quadrature component in baseband; and    providing a phase correction to reduce the phase imbalance by controlling the phase of a first signal of the three signals independent of a second signal of the three signals.    
   
   
       18 . The method according to  claim 17 , wherein detecting the phase imbalance comprises: 
 converting the in-phase component in baseband to a digital in-phase feedback component;    converting the quadrature component in baseband to a digital quadrature feedback component; and    measuring the phase imbalance between the digital in-phase feedback component and the digital quadrature feedback component.    
   
   
       19 . The method according to  claim 18 , wherein providing the phase correction comprises: 
 generating a compensation signal based on the phase imbalance;    generating a tuning signal based on the compensation signal; and    varying the quadrature local oscillator signal based on the tuning signal to reduce the phase imbalance.